YouTube.com has made uploading and sharing video clips online simpler, writes Jim Colgan in New York

When it comes to video, what's the difference between TV and the web? Not very much if enthusiasts of the latest internet phenomenon are to be believed.

Websites that make forwarding video as easy as sending an e-mail are tearing down the barriers between the two media as popular shows end up online and so-called viral video ends up on the airwaves.

Industry watchers say the surge in the popularity of web video is forcing traditional broadcasters to reinvent themselves and, in a bid to stay relevant, television networks in the US are starting to embrace the internet as a new distribution channel.

"It's changing more than just the habits. It's changing the entire nature of networks and television," says Jeff Jarvis, a media consultant who writes the blog Buzzmachine.com.

Video on the web has been around for years, but Jarvis says there has been a shift in the phenomenon in recent months, thanks mainly to the emergence of one site. YouTube.com was set up by a pair of computer programmers who wanted to make it easier to pass on video they thought others should see.

Unlike more cumbersome tools such as Bittorrent or Limewire, which requires special software, they created a way for video to be viewed directly on the web.

Key to its success was the ability to send on the link via e-mail and now the site is a conduit for more than 35 million video downloads a day.

The kind of video uploaded to these websites sets it apart from its offline counterpart. For one, it is shorter, with most clips lasting just a few minutes. Some of the most watched include parodies, like a send-up of the social network Myspace.com and several spoofs of the film Brokeback Mountain.

Other videos consist of trailers from much-anticipated films (and from savvy film studios who upload them). Some advertisements have also "gone viral", as users describe it, the most popular being a Nike ad featuring the Brazilian soccer star Ronaldhino.

But the biggest difference is with the selection of video. Instead of producers choosing which programmes to broadcast, the video highlighted on YouTube and other sites is determined primarily by how many downloads it gets. Jarvis says this "democratisation" of content is part of a larger trend in user-generated content online.

There are now dozens of video sites with similar features such as iFilm and MetaCafe and some search engines like Google and Yahoo now include video components.

The content is almost entirely user-generated, so the video consists mostly of amateur recordings, but it also includes programmes taken directly from broadcast television. And this aspect of the growth is causing television executives to take notice of the phenomenon.

"They are trying to figure out where they stand in relation to this," says Steve Safran, the managing editor of a weblog about the TV industry called Lost Remote.

"The networks have been built on control and now they don't have any of that."

In a mark of the continuing battle between online and offline programmers, last December one network tried to assert its control. A YouTube user uploaded a clip of a comic rap song called "Lazy Sunday" which had played on the NBC show Saturday Night Live.

The clip was downloaded five million times before the network ordered it taken down, citing copyright infringement. But at the same time it started to disappear from YouTube, NBC made the video available on its own website where viewers were subject to the network's advertisements and they offered it for sale on Apple's iTunes service.

Such copyright issues have become common for these web video sites. More recently, a cable channel cancelled a controversial episode of South Park, but copies of the animated show ended up on YouTube. The site says it can't be blamed for copyright problems because it doesn't create the content and has little control over what its users upload.

While the television networks speak out about the growing web video phenomenon, they often benefit from the promotion. Shows like South Park have expanded their viewer base online and analysts point to an increase in TV viewers for Saturday Night Live that they say resulted from people forwarding the clip online.

In fact, some are saying the networks might have a hand in the videos ending up online themselves.

"There's a certain amount of evidence that suggests the marketing departments of these networks are either enjoying or are maybe involved in uploading the shows to get the attention, and then their legal departments are taking them off," says Safran, who is also an executive producer at a cable channel in New England.

Some networks are adopting different strategies to take control of their content.

This week, Disney, which owns the ABC television network, started streaming its most popular shows on its website. While the programmes will be free to watch, viewers will not be able to download or skip through the advertising.

Like other networks, ABC already offers its shows for sale through iTunes, but it is doubtful that these moves will stop viewers on sites such as YouTube from substituting the television with web video.

"They are trying to hold back the tidal wave, but they're doing it with a napkin," Safran says.

Others think the recent moves have more significance.

"I believe ABC's step was a huge one," says Jarvis. "But it was only a step."

Jarvis says that there will come a time when viewers won't know the difference between online and offline programmes.

Although Safran agrees programming will adapt, he says the two forms will always be different.

"Too many people think convergence will bring all these media together, when really it's divergence," he says.

Whether they converge or not, the influence of online video is showing up on conventional TV right now.

The music channel VH1 has a weekly show based entirely on clips from the web and a number of channels are about to follow suit.